394 A MONOGRAPH OF THE 



also varies considerably, sometimes it is obsolete, but 

 usually it is more or less apparent, and occasionally very 

 strongly developed. The small portion of membranous 

 structure remaining attached to the skeleton is rather stout, 

 and but sparingly furnished with the slender acerate spicula. 

 The general arrangement of the symmetrical portion of the 

 skeleton is very like that of Clialina seriata, but the absence 

 of horny fibre, and the peculiar form of the skeleton spicula 

 in Isodidya anomala, readily serves to distinguish it from 

 the former species, even though in their live state their 

 form and colour should prove to be perfectly similar. I am 

 indebted to my kind friend, the late Mrs. Griffiths, for this 

 interesting species. 



The deeper portions of the structures are very confused, 

 assuming much the appearance of a coarse stout Hali- 

 chondria, so that with our present very limited knowledge 

 of the natural extent of the interior portion of the sponge, 

 it becomes very difficult to say whether the regular interior 

 or the regular exterior portion of the structure should have 

 the greater influence in the determination of its generic 

 disposal; under all the circumstances of the case, I have 

 thought it advisable to refer it, in accordance with its ex- 

 terior portion, to the genus Isodictya. 



The surface of the sponge is even, and the whole of the 

 dermal membrane appears to have been removed by long- 

 continued maceration, but the present surface is thickly 

 furnished with porous passages, and there is one large, 

 slightly depressed oval osculuni, near the middle of the 

 outer surface, about the eighth of an inch in length. 



The fasciculi of the skeleton are very stout. 



14. IsoniCTYA SIMPLEX, BowerbatiTc. 



Sponge. Sessile, massive. Surface even, or more or less 

 tuberous, hispid. Oscida simple, disposed on the 

 sumn)its of the tuberous elevations, large. Pores 

 conspicuous. Dermal membrane aspiculous. Skele- 

 ton. Compact and regular ; primary lines multispicu- 



